The IP is entitled to charge those fees Aaron, as he will have quite a lot of work to do in proposing your variation and then closing the case - but anything is worth a try. The £500 relates to all disbursements relating to the case - cost of registration, bordereau, room hire, printing postage and stationery or any travel costs he has incurred. it seems a reasonable sum to me, and would have been one that you agreed to when you signed the proposal.
I would certainly try the lower offer if I were you - and don't forget it is your application for variation and not the IP's so insist it is put forward if you think that you are making a fair offer for the right reasons.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
To have me propose an IVA for you, please visit:
http://www.melaniegiles.com/ivaEnquiry.asp
See customer feedback at:
http://www.iva.com/iva_companies/IVA_Advice_Bureau.asp